Abstract

Nanocrystalline silicon suboxides (nc-SiO{sub x}) have attracted attention during the past years for the use in thin-film silicon solar cells. We investigated the relationships between the nanostructure as well as the chemical, electrical, and optical properties of phosphorous, doped, nc-SiO{sub 0.8}:H fabricated by plasma-enhanced chemical vapor deposition. The nanostructure was varied through the sample series by changing the deposition pressure from 533 to 1067 Pa. The samples were then characterized by X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Raman spectroscopy, aberration-corrected high-resolution transmission electron microscopy, selected-area electron diffraction, and a specialized plasmon imaging method. We found that the material changed with increasing pressure from predominantly amorphous silicon monoxide to silicon dioxide containing nanocrystalline silicon. The nanostructure changed from amorphous silicon filaments to nanocrystalline silicon filaments, which were found to cause anisotropic electron transport.

The data on fabrication of silicon layers on various substrates by plasma enhanced chemical vapor deposition from the (silicon tetrafluoride)-hydrogen system are reported. The emission spectra of the plasma in the system are recorded. The samples were studied by the X-ray diffraction and secondary ion mass spectrometry techniques. The morphologic properties of the surface are examined, and the Raman spectra, the transmittance spectra in the infrared region, and photoluminescence spectra are recorded. The phase composition of the layers corresponds to nanocrystalline silicon, in which the dimensions of coherent-scattering grains vary with the conditions of the preparation process in the rangemore » from 3 to 9 nm. The layers exhibit intense photoluminescence at room temperature.« less

The mechanical stress in plasma enhanced chemical vapor deposited SiO{sub 2} and SiN layers is investigated. The dielectric films are deposited on Si and GaAs substrates, respectively. A first annealing of the samples yields irreversible structural changes of the films due to a loss of water and hydrogen. The elastic constant and the thermal expansion coefficient of the densified SiO{sub 2} layers are estimated by temperature dependent curvature measurements to be E{sub c}/(1-{gamma}{sub c})=1.0 {plus_minus}0.1x10{sup 12} dyn/cm{sup 2} and {alpha}{sub c}=(0.6{plus_minus}0.2)x10{sup {minus}6}{open_quotes}C{sup {minus}1}. IR absorbance measurements show a dependence of the center frequency of the Si-O bond-stretching vibration on themore » total film stress. Correlating the strain deduced from this measurement with the total film stress yields an elastic constant of about E{sub c}/(1-{gamma}{sub c})=(3{plus_minus}1)x10{sup 11} dyn/cm{sup 2}. The physical fundamentals of this measuring method as well as the temperature dependent measurements are discussed in detail to explain the apparent discrepancies in the estimation of the elastic constant. These considerations show that the true elastic constant of the SiO{sub 2} film can only be estimated by the temperature dependent measuring method. 18 refs., 6 figs.« less

This paper presents, for the first time, the successful integration of three rapid, low-cost, high-throughput technologies for silicon solar cell fabrication, namely: rapid thermal processing (RTP) for simultaneous diffusion of a phosphorus emitter and aluminum back surface field; screen printing (SP) for the front grid contact; and low-temperature plasma-enhanced chemical vapor deposition (PECVD) of SiN for antireflection coating and surface passivation. This combination has resulted in 4 cm{sup 2} cells with efficiencies of 16.3% and 15.9% on 2 {Omega}-cm FZ and Cz, respectively, as well as 15.4% efficient, 25-cm FZ cells. Despite the respectable RTP/SP/PECVD efficiencies, cells formed by conventionalmore » furnace processing and photolithography (CFP/PL) give {approximately}2% (absolute) greater efficiencies. Through in-depth modeling and characterization, this efficiency difference is quantified on the basis of emitter design and front surface passivation, grid shading, and quality of contacts. Detailed analysis reveals that the difference is primarily due to the requirements of screen printing and not RTP.« less

In this work, a-Si:H films with good electronic properties in spite of an inhomogeneous structure were prepared by the 55 kHz plasma enhanced chemical vapor high-rate deposition technique. The structural analysis using infrared spectroscopy and atomic force microscopy has shown that these films possess two dominant types of microstructural inhomogeneities, which differ by size. To analyze the influence of a 55 kHz plasma on the properties of intrinsic a-Si:H film, the density of states in the a-Si:H mobility gap was estimated by modeling of the temperature dependence of the photoconductivity and from electron paramagnetic resonance measurements. Investigated capacitance-voltage characteristics showedmore » that a-Si:H/c-Si heterostructures have low interface density of states and can be considered as an ideal abrupt heterojunction.« less